Whatever you say... I guess if you get longtubes and they don't fit, you can't say I didn't tell you so.
I read wrong anyway, those are truck headers "Headers, Full-Length, Steel, Painted, Chevy, GMC, SUV, Pickup, Small Block, Pair" Summit Racing SUM-G9006 - Summit RacingĀ® Headers - Overview - SummitRacing.com
That came up when I searched for 00 GP headers.